IOWA CITY, Iowa (AP) -- Thermal imaging shows hot spots remain possible obstacles to cleanup efforts after the landfill fire in Iowa City.

Landfill superintendent Dave Elias told the Iowa City Press-Citizen that the extremely dry conditions led to cracks in dirt layer used to smother the fire. The cracks let air reach the smoldering material below and cause a number of flare-ups.

The cleanup work began last week and could take two months. Ash and debris will be uncovered and removed. Any smoldering materials will be extinguished.

The fire began May 26 on roughly 7 1/2 acres, primarily in an unused portion. The fire spread to a layer of shredded tires used for drainage. The fire cause hasn't been determined.